Random guitar pedal board design
Background
This is a personal toy project that has gone through several phases, but the common theme has been that it makes absolutely no sense outside of the very specific niche of "Linus is trying to learn random things about electronics".
So keep that in mind: there is very little point to any of this to anybody else. Don't expect some great useful guitar pedal experience.
I call it my "LEGO for adults" hobby, because this got started when I wanted to extend my traditional after-Christmas activity (which was receiving and building actual LEGO kits, which has been a thing for me since I was a wee tyke) with something else.
So for Christmas 2024, I got a new soldering iron and randomly started doing guitar pedal kits. And so over the next month or two, I built at least two dozen kits, and had to literally look for victims to give them away to because I had no use for them myself.
Note Of all the kits I built, the ones I enjoyed the most were the Aion FX ones, and if you are looking for a kit build of traditional analog guitar pedals, I can heartily recommend them. The documentation, the customer service, the components, and the enclosures were all top notch. See "Aion FX"
Anyway, after building a lot of these traditional analog guitar pedal kits I decided I really wanted to actually understand what they did, because I really had very little experience with any analog circuits.
While I've done some very limited electronics most of my life, almost all of it has been related to computers, so it's been either digital logic or power supplies for them.
Also, I was looking for a different kind of soldering experience where there was less snipping of legs of through-hole components. I actually like soldering SMT components, but that doesn't tend to be what those guitar pedal kits do.
I had done some very limited PCB design with kicad a few years ago, so I decided to just start learning more about analog circuits. And then it kind of grew from that.
Electrical design
This is the "fourth generation" of my guitar pedal design journey, and is a new repository because the goal of the learning experience has evolved.
What started out being about the analog circuits (and the power rails: those were always a big thing) got to the point where I realized I really want to do a mixed signal design: understanding what the circuits do is one thing, re-creating some analog design from the 70s when you don't actually care about the sound is another thing entirely.
Also, on the actual analog signal side, I started out using op-amps, but as I was attempting to learn how things actually worked, I had switched over to a "discrete components only" model, and this continues that trend (except for the whole digital side, of course).
Note To me "discrete components" does include more optimized packages: things like dual diodes or matched transistors, but not more complex circuits like a op-amp (or a 555 timer or D Flip-flop or other classic logic IC)
Also, because I don't typically listen to the end result, but look at it with a signal generator and an oscilloscope, I've grown to detest power supply noise.
Not knowing what I was doing, quite a lot of my circuits have been very noisy indeed, and have coupled in noise from the power supply into the signal chain, and you can really see that on an oscilloscope even when it's not always audible.
Even in op-amp designs, where the op-amp itself has a very high PSRR and isn't mixing power supply noise into the signal, my biasing circuits were often not great, and so the op-amp would see not just the signal but the power supply noise coming in through the DC biasing.
And every time I tried a dual power rail (so that I could just keep the signal ground-referenced), the noise from the switching ended up just always noticeable, and the extra complexity was annoying when a lot of effects then didn't have any real use for the dual rail.
Filtering obviously helps, but this is just a long-winded explanation for why I ended up really appreciating the "bias to ground" JFET model for the signal input side, and the common drain follower in particular.
That works with a single JFET (the MMBF5103 worked well for me), but my favorite design so far is a dual-JFET LS844 with the second matched JFET used as a current sink. It has basically infinite input impedance (and could be DC coupled, although I do the coupling capacitor with resistor to ground) and gives a good output signal somewhere roughly in the middle of the single-supply 9V rail.
See LS844 Application note
Why do I mention this in particular? Mainly because it's a great example of how completely insane my designs are. That LS844 is used as a voltage follower with a noticeable DC offset, and that single dual-JFET SOT-23-6 component is more expensive - and harder to find - than a simple op-amp would be.
Just to put that into perspective: you can buy LM358's at mouser for about $0.07 each in reasonable quantities (ie a hundred). Sure, that's not the greatest op-amp ever and you'd have to have a 5V regulator, so maybe you're better off at twice the cost, and go for a TL082 or a TL072 instead. Or go for a BJT input one and be even cheaper.
The LS844? Harder to find, and much more expensive. If they are in stock at all, you'll find them for $2.50 when you buy ten or more. And I'm using it as a questionable replacement for a single input of one of those dirt-cheap op-amps.
Put another way: go elsewhere for sane designs. This is not the place.
But it does work quite well. See some notes on the signal path testing here
Physical design
I started out with small designs that I decided would fit best into a 1590A enclosure (basically the smallest regular guitar pedal form factor), because it was cute. The purely physical layout limitations were actually interesting, and since I was doing SMT components and simple circuits, the circuit sizes were never even remotely an issue.
However, as I decided that I don't want to play around with silly analog audio effects from the 60's and 70's any more, that 1590A enclosure got increasingly painful. Putting an Electrosmith Daisy Seed inside of them is possible, but only if you don't do a proper stomp-switch and limit yourself to two pots. And yes, I did that.
Do I want to use the pre-built Daisy Seed? Maybe - and maybe not. This repository does include the beginnings of a "what if I did my own version of a MCU and CODEC", because it's an interesting learning experience too. And I started that because then I'd be able to fit things better in a 1590A.
But then my meds kicked in, and I've finally given up on the 1590A. It's cute. The mechanical challenges were interesting. But they've gone from "interesting" to "overly limiting".
So now I'm instead doing a much more reasonable enclosure. So 1590B it is. That just simplifies things a lot and the end result is a lot saner.
Components
I've used JLCPCB, PCBWAY and OSH Park for PCB manufacturing. The end results are all good, pick the one you're most comfortable with. I've found that at least for me, JLCPCB gives the fastest turnaround time, but I suspect it heavily depends on where you live.
In the past, I've done some PCB assembly services too, and PCBWAY did a good job. With this project where the manual soldering has been part of the whole experience, I've just done bare boards so far.
I've toyed with the idea of doing some assembly service jobs in case I decide to go for more fiddly components, but that's really for a future "what if I do the digital side too". I'm not there yet.
Connectors and potentiometers are typically from Tayda Electronics, with most of the actual common SMD components from kits or from Mouser.
Some typical parts from Tayda:
For "random" SMD capacitors and resistors, get one of the kits. I can personally heartily recommend the Guanruixin kits from Amazon: there are 0805 and 1206 kits of both capacitors and resistors, and I love the packaging and labeling. Very good for organizing at a hobbyist level.
Just the storage case makes them worth getting:
There are other kits out there, but it's nice to have a good compact case with a selection of various values. If you are like me, you'll run out of the common resistor values, and then I buy cut tape from Mouser and just fill the specific compartments in that kit case.
Which brings us to Mouser and DigiKey and the like: not just for refills, but for anything that is slightly more specialized. Like that LS844, but really most of the not-completely-standard SMD components.
My exact SMD component choices have been pretty random, and a number of them have been influenced by footprint rather than technical merit. I tend to like things like dual transistor SOT-23-6 packages, and if you look at my MOSFET choices I think you'll find that the primary choice was packaging and a high enough V GSS .
Put another way: I'm not claiming my parts choices necessarily make sense. They've worked for me - often in the sense of "that other part was just too fiddly to solder, so I've replaced it with this other part that works for me"